Method for making a radiation heating structure

ABSTRACT

The invention concerns a method for making a radiation heating structure comprising a heating film electrically powered to produce Joule heating, a radiating film comprising radiating additives and a thermally insulating film. The insulating film and the radiating film are fixed on either side of the heating film. The structure is obtained by double injection of polymerizable resins in a heating mould, a first resin being filled with radiating additive on the side of the heating film and a second more fluid resin on the side of the insulation.

FIELD OF INVENTION

The invention relates to the field of heating elements, such asradiation heating panels.

BACKGROUND OF THE INVENTION

Heating structures of this type, which are substantially in the form ofa sheet, comprise a heating layer that includes at least one electricalresistor intended to be electrically powered in order to produce Jouleheating. This heating layer is advantageously fixed between tworeinforcement layers that are preferably electrically insulating.

The heating layer is fixed between the two reinforcement layers byinjecting a resin that is cured when the temperature is raised, therebyalso stiffening the heating structure obtained.

To give this structure thermal radiation properties, the injected resinis filled with radiating additives, such as plaster particles.

However, the resin thus filled, once cured, does not allow theaforementioned reinforcements and/or electrical resistor to besatisfactorily bonded, and debonding of one element of the heatingstructure, when in service, has often been observed.

The present invention aims to improve the situation.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a radiation heatingstructure, comprising at least:

-   -   a heating layer comprising at least one electrical resistor        intended to be electrically powered in order to produce Joule        heating;    -   a radiating layer, comprising predominantly radiating additives;        and    -   a substantially thermally insulating layer, the insulating layer        and the radiating layer being placed on either side of the        heating layer.

Advantageously, this heating structure is substantially in the form of asheet, with an insulating face and, opposite it, a radiation heatingface. The term “in the form of a sheet” denotes both a plane form and asubstantially curved, or even bent, form.

The present invention also proposes a process for manufacturing such aheating structure, in which:

-   -   a) a laminate comprising at least the aforementioned electrical        resistor and reinforcements is introduced into a mold; and    -   b) injected into the mold:        -   via an opening formed in a first wall of the mold opposite            one face of the laminate intended to form the radiating            layer, is a first resin that is filled with radiating            additives and can be cured in the mold; and        -   via an opening formed in a second wall of the mold opposite            one face of the laminate intended to form the insulating            layer, is a second resin that is more fluid than the first            resin and can be cured in the mold.

The insulating character of the thermally insulating layer isadvantageously conferred by an insulating sheet that is introduced withthe aforementioned laminate into the mold so as to face the second wallvia which the more fluid, second resin is injected. Additionally, or asa variant, the second resin may include insulating additives and,despite the presence of such insulating additives, may still be morefluid than the first resin.

In one advantageous embodiment, the manufacture of the heating structureis carried out by pultrusion and the aforementioned mold is a pultrusionmold having an entry end and an exit end, between which, in step b),said laminate is made to advance while the first and second resins arebeing injected. Preferably, this advance is sufficiently rapid to limitany diffusion of the radiating additives into the second wall of themold.

In a preferred embodiment, the respective injection rates of the firstand second resins are chosen according to the speed of advance of theaforementioned laminate through the pultrusion mold and so as to limitany diffusion of the radiating additives into the second wall of themold, while ensuring diffusion of the radiating additives into theheating layer.

The object of the present invention is also a mold for implementing theprocess, which mold comprises:

-   -   a first wall and a second wall opposite said first wall;    -   first means for injecting a first resin, which can be cured in        the mold and is filled with mineral additives, via a first        opening in the mold formed in said first wall; and    -   second means for injecting a second resin, which can be cured in        the mold and is more fluid than the first resin, via a second        opening formed in said second wall.

In a preferred embodiment, this mold is a pultrusion mold and includes,for this purpose, an entry end and an exit end, between which theaforementioned laminate can advance.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent onexamining the following detailed description and the appended drawingsin which:

FIG. 1 shows schematically a heating structure S within the meaning ofthe present invention;

FIG. 2 shows schematically a cross-sectional view (along the line ofsection II-II) of the heating structure S of FIG. 1;

FIG. 3 shows schematically a pultrusion installation for the manufactureof heating structures; and

FIG. 4 shows schematically the heating structure S advancing through apultrusion mold 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring firstly to FIG. 1, the heating structure S has the generalform of a substantially curved sheet. The heating structure S iselectrically powered via at least one connection module Ml provided onan end edge of the heating structure S.

This heating structure S may be intended for heating domestic rooms, ashome radiators connected to the electrical mains. In other applications,the heating structure S may be used as a reinforcing structure (such asa reinforcing beam, or else a plinth) in industrial or domesticpremises, or even in public places. In such an application, a pluralityof heating structures S, in the form of heating panels, may for examplebe provided, these being joined to one another via electrical connectionmodules M1 and M2, in order to form the covering of a wall, or else anumber of reinforcing beams for a construction, either in industrialpremises or in a public place (a bus shelter or the like).

The heating structure S may be of not insignificant benefit in otherapplications, such as heated stadium seats or as home bathtubs (thusallowing water to be kept at the desired temperature).

Another particularly advantageous application is in the automobilefield. A radiation heating structure of the type shown in FIG. 1 may beused for demisting a windshield, such a structure forming an integralpart of or acting as the dashboard of the passenger compartment of amotor vehicle, or else acting as side reinforcements in the passengercompartment.

Referring now to FIG. 2, the heating structure within the meaning of thepresent invention comprises a heating film FC sandwiched between tworeinforcement layers C1 and C2. Each reinforcement layer C1 and C2comprises an array FV of glass or carbon fibers, each embedded inrespective resins R1 and R2, which cure when the temperature is raised,for example in a pultrusion mold as will be seen later.

More particularly, the reinforcement layer C1 comprises a resin R1filled with particles P which act as radiating additives. For example,such radiating additives may be iron, aluminum, wood or vermiculiteparticles. In an advantageous embodiment, these particles are mineralparticles, such as marble particles. In a preferred embodiment, theseradiating additives are plaster particles, the plaster having at leastthe following advantages:

-   -   at high temperature, it releases water, giving the heating        structure S a flame-retarding effect;    -   it is of low cost;    -   it increases the stiffness of the structure; and    -   its heat radiation properties give the heating structure S its        desired radiating character.

Thus, such pulverulent additives, with a high emissivity, give theheating structure S radiation heating properties. The application ofsuch a radiating structure S is advantageous in (but not limited to)open public areas in which a flow of air is regularly circulating andfor which convective heating would be prohibitively expensive. Inaddition, radiation heating provides the feeling of soft heating, withno air mixing, by emission of electromagnetic waves in the infraredrange. On receiving these waves, the walls, floors and other elements ofa room “convert” them into heat.

In the abovementioned applications of the heating structure according tothe present invention, it is preferable for the structure S to radiateonly via one of its faces F1 so as to limit the electrical consumptionand thus maintain a satisfactory degree of conversion of electricalpower into heat. For this purpose, the heating structure S furthermoreincludes an insulating layer IS on its face F2, opposite the radiatingface F1. For example, the insulator IS may be a sheet of mineral wool,such as glass wool or, preferably, rock wool.

The heating film FC contains at least one electrical resistor. For thispurpose, said heating film FC may be formed from a plastic film on whichone or more resistors have been screen-printed. As a variant, it is alsopossible to envision using carbon fiber fabric. In yet another variant,there may be an array of conducting wires. In general, it should bepointed out that the heating film FC is formed from one or more types ofelectrically resistive materials intended to be electrically powered andcapable of producing heat by the Joule effect when an electrical currentflows through them.

Advantageously, the use of a carbon fiber fabric ensures satisfactoryimpregnation of the resins R1 and R2 in which it is embedded, therebymaking it possible to achieve good adhesion of the heating film FC inthe heating structure S.

Thus, in the embodiment in which the heating film is a screen-printedfilm, it is advantageous to provide openings made in the film. Theresins R1 and R2 can then interpenetrate during the in-mold injectionstep.

Moreover, it is also possible to provide a heating film FC produced inthe form of a fabric of fibers, for example glass fibers, in whichfabric an electrically conducting wire is overstitched, or else thefibers of which are impregnated with a conductive polymer.

The radiating composite section that the heating structure S thus formshas a first face F1 with a high radiating power and an insulating secondface F2, opposite the first one, while the reinforcements FV provide thestructure S with satisfactory mechanical strength. The particles P,which are preferably plaster particles and are predominantly in theradiating reinforcement layer C1, ensure both a high emissivity and goodmechanical strength of the structure S. In FIG. 2, it should be noted inparticular that the reinforcement layer C2, which includes the insulatorIS, contains substantially fewer radiating particles P than thereinforcement layer C1 intended to radiate. In the process formanufacturing the heating structure S within the context of the presentinvention, the first resin R1 is initially filled with particles P, inorder to form the radiating layer C1, whereas the more fluid resin R2contains no such radiating additives.

A process for manufacturing the structure S, by pultrusion in apreferred embodiment, will now be described with reference to FIG. 3.

The pultrusion process allows the manufacture of polymer-matrix sectionsreinforced with continuous reinforcements. The reinforcements, such ascarbon or glass fibers or fabrics FV, come from bobbins B placed onsupports at the front of the pultrusion machine. Moreover, the heatingfilm FC, in an embodiment in which it is in the form of a carbon fiberfabric, and the insulating sheet IS, in the embodiment in which it is inthe form of a rock wool sheet, are placed on supports that give it afreedom of rotation so that all of the bobbins are unwound continuously.Guides and racks 2 orient the fibers, the heating film and theinsulating sheet, by placing them under substantially the same tensionin order to constitute the backbone of the future composite forming thestructure S. Thus presented in an organized form, they are impregnatedwith resins R1 and R2 at the entry of a die 1, which ensures that thewhole assembly is held together and the resins are cured by heating.This die therefore has the shape of a heating mold (hereinafter calledthe “pultrusion mold”), into which the aforementioned first resin R1 andsecond resin R2 are injected. These first and second resins harden bycuring in the pultrusion mold. The various constituents advance alongthe X axis by means of a traction device 3 located downstream of thepultrusion mold 1. The station 4 of the pultrusion installationcomprises a cutting and ventilation device for thus recovering theheating structure S for which it now remains only to provide one or moreconnection modules M1 and M2 for connecting its heating film FC.

Advantageously, the resins injected (arrows R1 and R2) into thepultrusion mold 1 are thermoplastics. In this embodiment, the station 4of the pultrusion installation may be preceded by a bending unit forbending the composite section output by the mold 1, so as to give it acurved or other such chosen shape. For this purpose, polymer matricesintended to form the protection layers C1 and C2, by impregnation of thecarbon or glass fibers or fabrics FV, may advantageously bethermoplastic resins of the PBT (polybutylene terephthalate) type orelse of the polycaprolactone type, allowing the structure output by thepultrusion mold to undergo a thermoforming operation.

Advantageously, the pultrusion makes it possible to obtain shapes ofsections that are both plane and curved, or else more complex shapes ofsolid or hollow cross section.

The description now refers to FIG. 4 in which the laminate LAM of FIG.3, formed by the insulating sheet IS, the heating film FC and the carbonor glass fibers FV, for example in woven form, is fed into the entry end10 of the pultrusion mold 1. The laminate, comprising the insulatingfilm IS and the heating film FC, placed among the reinforcement fibersFV, thus penetrates the mold in order to be impregnated with resins R1and R2. The two resins are then injected (arrows R1 and R2) via openings12 and 13 formed in the mold 1 on opposed walls and facing the heatingfilm FC and the insulating sheet IS, respectively. The resin R2 is astandard resin (of the PBT type or else of the epoxy or other type). Itis thus injected without radiating additives, in contact with thethermal insulation IS, into the upper portion of the mold 1.Satisfactory impregnation is thus guaranteed and better thermalinsulation is provided in this region of the heating structure S beingformed. The other resin R1 is injected into a lower portion of the mold1. The resin R1 is more viscous and is filled with radiating additivesin order to constitute the radiating matrix of the section. Preferably,the resin R1 substantially coats the heating film FC, whichadvantageously has openings in order to promote interpenetration of thetwo resins R1 and R2.

Preferably, the fluid resin R2 is injected via the opening 13 into anupper wall of the mold 1, whereas the viscous resin R1 is injected viathe opening 12 placed in a lower wall of the mold 1, thereby making itpossible, through gravity, to limit the contamination of the thermallyinsulating layer C2 by the radiating additives. Moreover, the respectiveflow rates of the resins R1 and R2 are controlled according to the speedof advance of the laminate LAM through the pultrusion mold 1, dependingon the radiating additive content of the resin R1 and depending on therate of cure of the resins at the temperature of the mold.

Typically, for a speed of the laminate through the mold of substantiallybetween 0.5 and 1 m/minute, a flow rate of the fluid resin R2 of about0.5 to 1.5 l/minute and a flow rate of the viscous resin R1 of about 0.5to 1.5 l/minute for a mass of about 900 kg of radiating additives per m³of resin of the thermosetting polyester type are provided. The resins R1and R2, of the aforementioned type, cure in the pultrusion mold 1 attemperatures of around 100 to 150° C.

The preformed heating structure S is withdrawn via the exit end 11 ofthe pultrusion mold 1 and advances to a bending unit equipped with apress comprising pressing members P1 and P2 for giving the structure S achosen shape by bending, in a preferred embodiment in which the resinsR1 and R2 are thermoplastics.

Finally, the process for manufacturing the heating structure S continueswith the fitting of a connection module M1 in order to electricallypower the heating film FC.

Of course, the present invention is not limited to the embodimentdescribed above by way of example—it extends to other alternativeembodiments.

Thus, it will be understood that, in a simplified embodiment of theheating structure S, one of the thicknesses of the reinforcements FV inthe layer C1 or in the layer C2 may be omitted. However, it isadvantageous to keep the electrically insulating reinforcements in theradiating layer C1. In this embodiment, a thickness of resin R2 may bemaintained between a thermally insulating sheet IS and the heating filmFC without reinforcements FV.

In the above embodiment, an insulating sheet IS is introduced into thelaminate which is embedded in the resins R1 and R2. In an alternativeembodiment, this insulating sheet may be omitted and the insulatingcharacter of the face F2 of the structure is provided by injecting aresin R2 that is itself filled with insulating additives, such asceramic particles. The resin R2, even filled with such insulatingadditives, remains more fluid than the resin R1 filled with radiatingadditives, such as plaster particles. Of course, it will be understoodthat the insulating face F2 of the structure may furthermore compriseboth an insulating sheet IS and a resin R2 filled with insulatingadditives of the aforementioned type, in applications in which it isadvantageous to optimize the insulation of the face F2 of the heatingstructure within the context of the invention. These insulatingadditives have not been shown in the figures for the sake of clarity,but they are predominantly close to the insulating face F2.

The process described above for manufacturing the heating structure S isadvantageously a pultrusion process. As a variant, composite sectionsfor forming the heating structure S may be produced by any other formingtechnique, such as reaction molding or RIM (Reaction Injection Molding),or compression molding, such as BMC (Bulk Molding Compound) or SMC(Sheet Molding Compound).

In particular, within the scope of the present invention, a simple moldfor injecting the resins R1 and R2 may be provided in which a laminatecomprising at least reinforcing fibers FV and a heating film FC are heldtaut. A viscous resin R1 filled with radiating additives P and a morefluid resin R2 are injected into this heating mold via two opposedopenings in order to consolidate all of the elements of the structure.

1. A process for manufacturing a radiation heating structure, thestructure comprising: a heating layer comprising at least one electricalresistor intended to be electrically powered in order to produce Jouleheating; a radiating layer; and a substantially thermally insulatinglayer, the insulating layer and the radiating layer being fixed oneither side of the heating layer, wherein: a) a laminate comprising atleast said electrical resistor and reinforcements is introduced into amold; and b) injected into the mold; via an opening formed in a firstwall of the mold opposite one face of the laminate intended to form theradiating layer, is a first resin that is filled with radiatingadditives and can be cured in the mold; and via an opening formed in asecond wall of the mold opposite one face of the laminate intended toform the insulating layer, is a second resin that is more fluid than thefirst resin and can be cured in the mold.
 2. The process as claimed inclaim 1, wherein said mold is a pultrusion mold having an entry end andan exit end and, wherein in step b), said laminate is made to advancebetween the two ends of the mold while said first and second resins arebeing injected, said advance being sufficiently rapid to limit anydiffusion of the radiating additives into the second wall of the mold.3. The process as claimed in claim 2, wherein the respective injectionrates of the first and second resins are chosen according to the speedof advance of said laminate through the mold and so as to limit anydiffusion of the radiating additives into said second wall of the mold,while ensuring diffusion of the radiating additives into the heatinglayer.
 4. The process as claimed in claim 1, wherein said laminatefurthermore includes a thermal insulator intended to he embedded in thesecond resin, this thermal insulator being placed, in said laminate,facing said second wall of the mold in order to form said insulatinglayer.
 5. The process as claimed in claim 1, wherein, when theinsulating layer and the radiating layer are each reinforced, saidlaminate comprises: reinforcements; at least one electrical resistor;and reinforcements.
 6. The process as claimed in claim 5, taken incombination with claim 4, wherein said laminate comprises:reinforcements; at least one electrical resistor; reinforcements; and athermal insulator.
 7. The process as claimed in claim 4, wherein thethermal insulator is a sheet of mineral wool, such as rock wool.
 8. Theprocess as claimed in claim 1, wherein the second resin includesinsulating additives.
 9. The process as claimed in claim 1, wherein theradiating additives are plaster particles.
 10. The process as claimed inclam 1, wherein said reinforcements are fibers, such as glass fibers.11. The process as claimed in claim 1, wherein said electrical resistorconsists of a network of metal wires.
 12. The process as claimed inclaim 1, wherein said electrical resistor consists of a fabric of atleast partly electrically conductive fibers.
 13. The process as claimedin claim 1, wherein said electrical resistor consists eta screen-printedfilm.
 14. The process as claimed in claim 1, wherein said first andsecond resins are thermoplastics.
 15. A mold for implementing a processfor manufacturing a radiation heating structure, wherein the moldcomprises: a first wall and a second wall opposite said first wall;first means for injecting a first resin, which can be cured in the moldand is filled with radiating additives, via a first opening in the moldformed in said first wall; and second means for injecting a secondresin, which can he cured in the mold and is more fluid than the firstresin, via a second opening formed in said second wall.
 16. The mold asclaimed in claim 15, wherein it furthermore includes an entry end and anexit end in order to implement said process by pultrusion.
 17. Aradiation heating structure having at least two external faces, whereinit comprises at least: a heating layer comprising at least oneelectrical resistor intended to be electrically powered in order toproduce Joule heating; a radiating layer comprising predominantlyradiating additives as a first external face; and a thermally insulatinglayer as a second external face, the insulating layer and the radiatinglayer being placed on either side of the heating layer.
 18. The beatingstructure as claimed in claim 17, wherein the structure is substantiallyin the form of a sheet, with an insulating face and, opposite it, aradiation heating face.
 19. The heating structure as claimed in claim17, wherein the insulating layer and the radiating layer includereinforcing fibers.